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A conceptual understanding of the T Test. . . some of these ideas are modified from Trochim, W. . . http://www. socialresearchmethod s. net/research/reshome. htm
Check out his web site. . .

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Presentation Transcript

The t-Test for Differences Between Groups :

The t-Test for Differences Between Groups

The t-Test :

The t-Test Tests whether the means of two groups are statistically different from each other

Statistical Analysis :

Statistical Analysis

Statistical Analysis :

Statistical Analysis Control
group
mean

Statistical Analysis :

Statistical Analysis Control
group
mean Treatment
group
mean

Statistical Analysis :

Statistical Analysis Control
group
mean Treatment
group
mean Is there a difference?

What Does Difference Mean? :

What Does Difference Mean?

What Does Difference Mean? :

What Does Difference Mean? Medium
variability

What Does Difference Mean? :

What Does Difference Mean? Medium
variability High
variability

What Does Difference Mean? :

What Does Difference Mean? Medium
variability High
variability Low
variability

What Does Difference Mean? :

What Does Difference Mean? Medium
variability High
variability Low
variability The mean difference
is the same for all
three cases.

What Does Difference Mean? :

What Does Difference Mean? Medium
variability High
variability Low
variability Which one shows
the greatest
difference?

What Does Difference Mean? :

What Does Difference Mean? A statistical difference is a function of the difference between means relative to the variability.
A small difference between means with large variability could be due to chance.
Like a signal-to-noise ratio. Low
variability Which one shows
the greatest
difference?

What Do We Estimate? :

What Do We Estimate? Low
variability

What Do We Estimate? :

What Do We Estimate? Low
variability Signal Noise

What Do We Estimate? :

What Do We Estimate? Low
variability Signal Noise Difference between group means =

What Do We Estimate? :

What Do We Estimate? Low
variability Signal Noise Difference between group means Variability of groups =

What Do We Estimate? :

What Do We Estimate? :

What Do We Estimate? The t-test, one-way Analysis of Variance (ANOVA) and a form of regression all test the same thing and can be considered equivalent alternative analyses.
The regression model is emphasized here because it is the most general. Low
variability